In this field of vertebral osteosynthesis, the correction or the immobilization of a portion of a vertebral column is achieved by means of several fixation implants (sometimes called connectors or anchoring plates) capable of cooperating with bone anchoring screws (or pedicular screws) and of rigidly connecting together rigid linking rods, in order to achieve the anchorage of these linking rods to the vertebrae.
In the case of the treatment of the lumbar spine, it is known to ensure an anchorage of the rigid linking rods on the sacrum, and even on both the sacrum and the hip bone. In this respect, it is necessary to use a fixation implant called sacroiliac fixation implant capable of cooperating with screws for anchoring on the sacrum (called sacral anchoring screws) and with a screw for anchoring on the hip bone (called iliac anchoring screw).
However, the forces subjected to the sacral and iliac anchoring screws require a particularly strong bone anchorage in the region of the sacrum in order to be able to resist the detachment of the screws and of the implants out of the bone.
It is known from the document WO 2013/153482 to propose a sacroiliac fixation implant composed of a sacral anchoring plate with two orifices for the passage of two sacral anchoring screws, a sacral connecting part intended to be mounted on one of the two orifices of the sacral anchoring plate and having a hole for the engagement of a linking rod, means for assembling the connecting part to the sacral anchoring plate, an iliac anchoring plate intended to be mounted on the other one of the two orifices of the sacral anchoring plate and having a hole for the passage of an iliac anchoring screw, as well as tightening screws.
The drawback of such an implant lies essentially in its complexity, multiplying the number of parts to assemble together (sacral anchoring plate, sacral connecting part, iliac anchoring plate, nuts and assembly means), such a multiplication of assemblies also contributing in increasing the dimensions, and especially the thickness or the overall height of the implant, and also in significantly increasing the time of the surgical intervention, not to mention the possible complications that this can entail.
It is also known from the document U.S. Pat. No. 5,133,717 to propose, in an embodiment illustrated in its FIG. 2, a sacroiliac fixation implant composed of a plate provided with three orifices for the passage of sacral anchoring screws and of an iliac anchoring screw, with a slotted boss provided with a threaded orifice for tightening a linking rod. Although this implant is somehow compact, it does not offer an optimum orientation for the anchoring screws which would allow for a sufficient and durable anchorage.